1. Field of the Invention
The invention relates to a working appliance, in particular a tamper for soil compaction or a hammer, with a tamping or beating working mass driven linearly back and forth, via a crank mechanism and a spring assembly, by a motor belonging to the upper mass.
2. Description of the Related Art
Known tampers of this type are designed in such a way that the upper mass comprises approximately two thirds and the beating working mass or lower mass one third of the entire tamper mass, whilst the distances covered in each case by the upper mass and the working mass are in inverse ratio to one another. In this case, the movement of the upper mass is of the order of magnitude of 25 to 30 mm.
This movement of the upper mass at a frequency of 10-11 Hz has adverse effects, because these vibrations are transmitted to the body of the person controlling the working appliance via a control handle, in particular to the person's hand and arm.
Although this transmission of vibrations to the body can for the most part be damped by the skilful attachment of rubber elements, there are nevertheless also high loads on the mounted drive motor, regardless of its design.
This problem also arises when the working appliance is mounted on other appliances or vehicles which may be seriously damaged by the vibrations occurring.
The output of the tamping system depends largely on the upper mass, since too great a working mass or too high a speed of the working mass moves the upper mass excessively and aggravates the problems described above.
These harmful effects can be partly inhibited by increasing the upper mass, but in this case the overall weight of the tamper is increased and the power consumption of the drive motor consequently rises.
DE-A 1 925 870 discloses a tamping appliance, in which a tamping foot can be driven, via a double crank mechanism, by a motor belonging to an upper mass. The drive power is distributed via gearwheels to two intermeshing crank disks which, via associated connecting rods, in each case drive rods connected to the tamping foot. Centrifugal weights are fastened in each case to the oppositely rotating crank disks, in such a way that the horizontal components of the centrifugal forces cancel one another, whilst the vertical components are added together and counteract the vibration acting on the tamper housing due to the vibration of the tamping foot. The arrangement described has to have a bulky design due to the provision of two rods connecting the upper mass to the tamping foot and due to the meshing crank disks. The overall weight of the tamper is considerable.